I like to take my hot sushi rice, add the vinegar/sugar mixture and spread it out on a sheet pan to let it cool. I then cut off strips of rice with my giant 10" spatula and drop it right onto the nori. It comes out perfect every single time!

My tuna awaiting cutting.

And for the rolls to be bite-sized, it really works better to use a half sheet of nori for each roll. I'm not sure sure why the sheets are the size they are.